Spinal column fixation device

ABSTRACT

Spinal column fixation device  1,  in the form of a pedicle screw, has an anchoring section  4  meant for fixation into a bone, and an adjoining head section  5  for attachment to a longitudinal support piece  3.  The head section  5  has an opening  7  that runs all the way through the part, transverse to the plane of symmetry  6  of the fixation device, for the purpose of admitting a tension-stable stable fastening device  2  which can be looped around longitudinal support piece  3.

FIELD OF THE INVENTION

[0001] This invention relates to a spinal column fixation device, inparticular a pedicle screw or pedicle hook adapted to be connected to alongitudinal support rod.

BACKGROUND OF THE INVENTION

[0002] For posterior spinal column correction, there are fundamentallytwo types of fixation or anchoring devices, pedicle screws and spinalcolumn hooks. As their name implies, pedicle screws are inserted intothe pedicle of the spinal column. Pedicle hooks can be attached eitherto the pedicle or to the lamina of the spinal body. They are placedprimarily in the thoracic area of the spine. For the most part, screws,which are inserted into the spinal body, are used in anterior spinalcolumn correction.

[0003] Spinal column fixation devices of this type in the form of apedicle screw are described, for example, in WO 92/03100.

[0004] The problem with all previously known spinal column systems fortreatment of spinal column deformities, is that their application iscomplex. This problem shows up primarily when the individual spinalcolumn fixation devices must be linked with a longitudinal supportpiece. In contrast to treatment of spinal column fractures, in treatingdeformities, several of the anchoring devices must be attached to thespinal column. Since the spinal column is deformed, only in very rarecases is it possible to place these anchoring devices in a line. Fromthis comes the problem of connection to a longitudinal support piecewhich normally consists of a round rod.

[0005] In the so-called derotation technique, the longitudinal supportpiece is pre-bent, and after attachment to the anchoring devices, turned90 degrees. This results in transformation of a lateral bending of thespinal column into a bending in the sagittal plane. In spite of theinitial enthusiasm for this technique, it has been determined that thelong term result is only a slight correction.

[0006] A correction of the spinal column which is optimal according tocurrent state of the art can be achieved with the so-called frametechnique. In this technique, the portion of the spinal column that isto be corrected is bridged by two longitudinal support pieces. Bothlongitudinal support pieces are attached to the spinal body adjacent tothe deformation. In accord with the type of correction desired, the twolongitudinal support pieces can be pre-bent. Into the spinal bodieswhich are bridged by the two longitudinal support pieces, anchoringdevices (pedicle screws or pedicle hooks) are attached. With the help ofthese devices, the individual spinal bodies can now be pulled toward thelongitudinal support pieces and attached.

[0007] In spite of its advantages relative to all previously knownmethods, this technique can very seldom be used, because the anchoringdevices do not possess sufficient adaptability. In addition to the axialloading, which is desired, they cause unnecessary bending loads, sincethey must be rigidly linked to the longitudinal support piece. Theseadditional loads are so great that at older defective locations in thespinal column, they can lead to a tearing out of the anchoring devices.This tearing-out problem occurs very frequently, since attachment of theanchoring device to the longitudinal rod can be done only in oneposition. That is, if the correction of the spinal column by its“ossification” is not 100% feasible, then this partially completedcorrection cannot be kept in this position. For this reason, often toomuch force is applied to achieve 100%, and indeed not because of thecorrection, but rather because of the required attachment of theanchoring devices to the longitudinal support piece. The onlyalternative is the intermediate insertion of a third longitudinalsupport piece, which must be attached to an existing longitudinalsupport piece via a connecting piece. This quantity of implants,however, often exceeds the biological tolerance limit and impairs thefunctioning of the spinal column musculature.

[0008] Presently known individual attachment devices (for example, inaccord with WO 92/03100) have an improved adaptation, but are at thetolerance limit especially in young patients, because of their size. Alarge size proves to be negative above all in complex corrections, sincealmost every spinal column which is equipped with such an implant, andthe spinal column musculature, suffers from it.

SUMMARY OF THE INVENTION

[0009] The present invention affords a remedy for this problem byproviding a spinal column fixation device which permits optimal choicesto correct the spinal column, while at the same time reducing the bulkof the implant to a minimum.

[0010] The invention provides a spinal column fixation device such as apedicle screw or hook comprising an anchoring element for fixation tothe bone, and a head section connected to the anchoring element, saidhead section comprising a transverse opening shaped to receive a tensionstable fastening element for attachment to a longitudinal support piece.

[0011] The invention also provides a spinal column fixation assemblycomprising a fixation device as described, a longitudinal support pieceand a tension stable fastening element shaped to extend through thetransverse opening in the head section and connect the device to thesupport piece.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will be further described with reference to thedrawings in which:

[0013]FIG. 1 is a view in front elevation and partially in verticalsection of a spinal column fixation device according to the invention inthe form of a pedicle screw, in a position to be attached to alongitudinal support piece by means of a fastening device.

[0014]FIG. 2 is a view in side elevation showing the device of FIG. 1.

[0015]FIGS. 3 and 4 are front and side elevational views, partly invertical section, of a spinal column fixation device according to theinvention with a double slot.

[0016]FIGS. 5 and 6 are front and side elevational views, partly invertical section, of spinal column fixation device according to theinvention with a laterally inclined longitudinal groove in the headsection.

[0017]FIGS. 7 and 8 are front and side elevational views, partly invertical section, of a spinal column fixation device according to theinvention with a miniaturized head section.

[0018]FIGS. 9 and 10 are front and side elevational views, partly invertical section, of a spinal column fixation device according to theinvention with a central hexagonal socket in the head section.

[0019]FIGS. 11 and 12 are front and side elevational views, partly invertical section, of a spinal column fixation device according to theinvention in the form of a spinal column hook.

[0020]FIG. 13 is a horizontal section through the spinal column hook ofFIG. 11, along the line B-B.

[0021]FIG. 14 shows schematically the spinal column hook of FIGS. 11-13attached to the bone which is pulled toward a longitudinal support pieceby a fastening device.

DETAILED DESCRIPTION OF THE INVENTION

[0022] Referring to FIGS. 1 and 2, a spinal column fixation assemblyaccording to the invention comprises a spinal column fixation device 1,a tension-stable fastening element 2 and a longitudinal support piece 3.The spinal column fixation device 1 comprises an anchoring element 4 forfixing into the bone (here in the form of a screw), and a head section 5connected to the anchoring element, which head section is meant forattachment to longitudinal support piece 3. The head section exhibits anopening 7 running all the way through it, and transverse to the plane ofsymmetry 6 of the fixation device, to admit the fastening element 2which can be looped around longitudinal support piece 3.

[0023] The tension-stable fastening element 2 for its part consists of abelt-shaped loop 9 closeable by a closing piece 8 and movable only inone direction, i.e. in a direction to make it smaller. By tighteningloop 9, it is possible to draw spinal column fixation device 1 closer tolongitudinal support piece 3, and optimally to bring it so that it iscontiguous with it. For this purpose, the head section 5, on its endintended to be adjacent to longitudinal support piece 3, is equippedwith a concave surface 10, which matches the convex surface of thelongitudinal support piece 3.

[0024] In FIGS. 3-8, various versions of the head section of spinalcolumn fixation devices are depicted.

[0025] In the design configuration according to FIG. 3, head section 5widens out to admit two separate openings 7 in the form of slots. In theversion of FIGS. 5 and 6, head section 5 is tipped down relative to theplane of symmetry 6, in order to bring it laterally closer tolongitudinal support piece 3. Finally, the version of FIGS. 7 and 8 hasa head section 5 that has been reduced in order to keep the implant sizeto a minimum.

[0026] In FIGS. 9 and 10, a spinal column fixation device 1 is depictedwhose head section 5 has a central hexagonal socket 11 running in thedirection of the plane of symmetry 6. This facilitates screwing thepedicle screw into the bone with a suitable hexagonal screwdriver.

[0027] In FIGS. 11-14, a spinal column fixation device 1 is depicted inthe form of a spinal column hook. This consists of an anchoring element4 for fixation into the bone, here formed as a two-sided blade, and anadjoining head section 5 for attachment to longitudinal support piece 3.The head section 5 displays two openings that run clear through thesection, and transverse to the plane of symmetry 6 of the spinal columnfixation device. These openings are to admit the tension-stablefastening device 2 which can be looped around longitudinal support 3.

[0028] The two-sided blade of the anchoring segment 4 is formed in sucha way that it encloses the pedicle 12 of spinal body 14.

[0029] From the foregoing it can be seen that a fundamental of thefixation device according to the invention is in the way in which theindividual spinal column fixation devices are coupled to a longitudinalsupport piece. In place of the previously used connections (which wererigid in all directions) between the fixation device and thelongitudinal support piece, the connection according to the invention isfixed only in the axial tension direction. That means that eachindividual spinal body is drawn toward the longitudinal support piece bytension. It does not matter whether 100% correction can be achieved ornot. Through the attachment, stable in the axial direction, of theattachment devices to the longitudinal support piece, the spinal columnis maintained in the corrected position. The force that acts on thespinal body during correction is like the action of a rope on the spinalbody. This has the additional advantage that during the course ofcorrection, the spinal body can seek its “path” on its own. Most of allthis has advantages in correcting long-term deformed spinal columns,since during the deformity which has continued over a long period thespinal elements have become deformed themselves and can becomeinterlocked into each other.

[0030] Forces which act axially on the spinal column are not transferredto the spinal column fixation devices, but rather are carried by thespinal bodies. If this is not desired, the axial forces as well as thetorsional forces can be transferred by a frame structure such as thatreferred to above. This frame structure consists of conventionalanchoring devices which are rigid in all directions; they are attachedto one or two longitudinal support pieces. Attachment of this frame isnot a problem, since in each case only two rigid fixation devices areconnected to each other. By displacement of the proximal fixationdevices to the distally attached fixation devices, the spinal columnarea within the frame can be relieved of loading. Torsional and axialloadings are carried totally by the frame. An elastic fixation of thespinal column, which has a healing influence on the spinal column, canbe achieved by long-extension bridging.

[0031] At the same time, the longitudinal support piece will protect thebone anchoring device interface (pedicle screw or spinal column hook)from being subjected to excessive loads. The fixation devices of theinvention will then be used within the frame, to effect the actualcorrection. The correction of the individual spinal bodies can be doneby degrees. In other words, each spinal element will alternate in beingdrawn to the longitudinal support piece in incremental fashion. Thisprocedure will avoid an overloading of the implant anchoring into thebone.

[0032] In addition to its improved functioning, the spinal columnfixation device according to the invention also is distinguished bybeing very simple to use.

[0033] As brought out above fixation devices according to the inventionmay have either one or two slots on their head sections, through each ofwhich an attachment device known in the technology as a cable binder ispassed. As described above, such tension-stable fastening devicesconsist essentially of a closed loop which moves via a locking piece inonly one direction, i.e. it can be reduced in size. Examples of suchfastening devices are described in detail in the German published patentapplications DE-A1 40 24 334 and DE-A1 40 21 246, where directapplication is made to bones, and not as a connecting piece between twoosteosynthetic structural elements.

[0034] As described above the head of the pedicle screw and pedicle hookaccording to the invention can be configured in various ways. If it hasbeen determined, with the aid of X-ray imaging, that a 100% correctioncan be achieved, then screws and/or hooks can be employed which possessa longitudinal groove on the head end that matches the longitudinalsupport piece. After correction has been carried out, the fasteningdevices in these pieces can be replaced by metal clasps. These metalclasps have an advantage in that they can, if necessary, accept forcesin all directions. Thus, in simple spinal corrections, a “frame” can bedispensed with if the need arises.

[0035] In another variant of the invention, the head of the fixationdevice is shaped so that the groove matches the longitudinal supportpiece placed laterally in the implant head. This head shape can be usedwhere the longitudinal support piece comes to lie laterally with respectto the anchoring device in its final position. Once again, X-ray imagingcan be employed beforehand to establish the final positions of thelongitudinal support piece and the anchoring device. As described athird head shape is configured in such a way that it has the smallestpossible dimensions, and possesses only the slot for receiving thefastening device. This anchoring device generally is used where smallimplant size is a priority, or where 100% correction cannot be achieved.

[0036] In another form, described above in connection with FIGS. 11-14,the spinal column fixation device, particularly where it is designed asa spinal column hook, has a double slot. Each slot, made on the headend, has different requirements. The slot placed before the tip of thehook serves to admit a “correction fastening device”. When thiscorrection fastening device exerts axial forces on the hook, the latterhas a tendency to tip downward, which causes it to hook more effectivelyinto the spinal body. The second slot serves to admit the “fixationfastening device”. This slot is located in the extension of the hookbase. After correction has been carried out, a fastening device isplaced through this slot to achieve improved stability of the hook.

[0037] Depending on the application, the spinal column fixation devicesas well as the longitudinal support pieces can be fabricated fromimplant steel, titanium, titanium alloys, plastics or biodegradablematerials. The same is true for the fastening devices. One preferredcombination of materials consists of titanium for the spinal columnfixation device and the longitudinal support pieces, and plastic for thefastening devices. This combination of materials has an advantage inthat with modern options for follow-up testing (MRI, CAT, etc.), it doesnot have negative effects.

What is claimed is:
 1. A spinal column fixation assembly comprising alongitudinal support piece having a longitudinal axis, a fixation devicehaving an anchoring element with a major axis for fixation to a bone anda head section formed as a single piece with said anchoring element,said head section having a channel for receiving said support piece anda slot extending through said fixation device along an axis transverseto the axis of a support piece positioned in said channel andintersecting the major axis of the anchoring element, said assemblyfurther comprising a tension stable fastening element extending throughsaid slot and around said support piece to secure said support piece insaid channel.
 2. The fixation assembly claimed in claim 1 , wherein theanchoring element, the head section, and the longitudinal support pieceare titanium and the fastening element is resorbable plastic.
 3. Thefixation assembly of claim 1 , wherein the assembly consists in itsentirety of titanium or a titanium alloy.
 4. The fixation assembly ofclaim 1 , wherein the assembly consists in its entirety of nonresorbable plastic.
 5. The fixation assembly of claim 1 , wherein saidfastening element comprises a belt formed in a loop and a closureelement in said belt and moveable along said belt in one direction only.